power consumption of nRF51822

[Amit Varshney]

Hi,

I'm using nrf51822 module purchased from www.waveshare.com/core51822.htm. I'm running uart over ble application example. I commented uart_init() function in main() because I dont want to print logs on a terminal. When I measured the power consumption in advertising state, It is arround 0.7mA. I measured this current using multimeter. I'm using 4AA duracell batteries which gives me a 6V. Then reduces that voltage to 3.3V using AMS1117 DC-DC converter. I want to know how to reduce the power consumption because I want to develope a device which run atleast 6 month on battery.

Thanx and Regards Amit

[Ole Bauck]

With the default advertising interval (40ms, defined in APP_ADV_INTERVAL) you may see current draw of up to 0.7mA (I measured 0.5-0.6mA on nRF51 DK using the latest SDK (v11) and SoftDevice (s130 v2.0.1). You can reduce this by increasing the advertisement interval. Also if connecting to the device the current consumption should go down.

You should not comment out uart_init() if you intend to use ble_app_uart as it depends on uart communication to send and receive data.

[Amit Varshney]

So, If i'm using default advertising interval then can you tell me what will be the battery life. I do not want to put the chip in system off mode because in my application I want the device will be ON everytime.

[Ole Bauck]

That will depend on the size of your battery. In theory this is the battery life:

Battery lifetime (h) = Battery capacity (mAh) / Average current consumption (mA)

Depending on the battery type it may be less since the battery capacity is specified for a constant low current draw while in BLE application the peak current draw may cut down on the capacity and hence the life. You can read this document if you want to know more about this.

The average current you have measured is in advertisement mode with interval 40ms. In your final product you may switch between different modes (advertising/connected), and then the current consumption will vary. The current consumption will also be dependent on the advertisement or connection interval as previously said.

[Amit Varshney]

Thanx Ole Bauck for that document. I want some suggestion from you. In my application, I want to drive a motor through nRF51822 which operates on 6V. I'm using 4AA duracell batteries, which gives me a voltage arround 6V. This voltage is goes to the motor driver. Then I converted that voltage to 3.3V using AMS1117 DC-DC converter to operate the nrf51822. I dont want to put the ble to stop advertising so I do not put it to system off mode. In this situation I measured a average current in advertising mode is arround 0.7mA. Is this a right way I'm doing this or some another way. Please help me in this.

[Ole Bauck]

That way is just fine. BTW: AMS1117 is an LDO regulator not a DCDC regulator/converter ;)